(1) Field of the Invention
The present invention relates to cross-linked, transparent gluten based polymers, and their method of preparation from grain flours. More specifically, the present invention uses film-forming solutions of gluten proteins obtained directly from grain flour which are cross-linked with a cross-linking agent which reacts with acidic and amino groups in the proteins. The transparent polymers particularly provide inexpensive, and biodegradable films and coatings.
(2) Description of Related Art
There are currently many polymer films used in industry. Although recycling programs have been developed, there is still a lot of waste of these single use products. Pollution by their very low degradation potential has elicited significant concern in the industry, government, and ecological groups.
Edible and/or biodegradable films and coatings have been developed using polymeric materials such as proteins (U.S. Pat. No. 3,653,925, to Anker et al, issued Apr. 28, 1972). There is currently limited applications for these films in the industry because of their poor water barrier and mechanical properties, as explained by Gennadios and Weller (Gennadios et al., Food Tech., 44(10):63 (1990)) and Krull and Inglett (Krull et al., Industrial uses of gluten, Cereal Science Today, 16(8):232 (1971)). In the development of edible and/or biodegradable films and coatings in which protein is used as the primary polymeric material, most of the current methods developed are based on U.S. Pat. No. 3,653,925, to Anker et al. This U.S. patent approaches the preparation of the film or coating by using dried wheat gluten (powder), available commercially or easily fabricated in a laboratory by various methods. In this case, vital wheat gluten (see AACC Method 38-20), which is a powder made from whole gluten, is rehydrated and a film-forming solution is formed after combination with other compounds. Examples of these methods include those by Gennadios et al (Gennadios et al., J. Food Sci., 58(1):212 (1993)), Gontard et al (Gontard et al., J. Food Sci., 58(l):206 (1993)), Gontard et al (Gontard et al., J. Food Sci., 57(1):190 (1992)), Gennadios and Weller (Gennadios et al., Food tech., 44(10):63 (1990) ), and Magnuson (Magnuson, K. M., Cereal Food World 30(2):17 (1985)). Another method of preparation is based on using whole gluten, as explained by Krull and Inglett (Krull et al., Industrial uses of gluten, Cereal Science Today., 16(8): 232 (1971)).
There have been some approaches to separating gluten and starch from wheat flour (U.S. Pat. Nos. 4,494,530 issued Jan. 22, 1985 to Jansma et al; No. 4,132,566 issued Jan. 2, 1979 to Verberne et al; 3,951,938 issued Apr. 20, 1976 to Kerkkonen et al; 3,574,180 issued Apr. 6, 1971 to Johnston et al; 3,542,754 issued Nov. 24, 1970 Fellers; U.S. Pat. No. 3,501,451 issued Mar. 17, 1970 Fellers; 3,498,965 issued Mar. 3, 1970 to Fellers and 3,493,384 issued Feb. 3, 1970 to Fellers). The disadvantage of some of these processes is that the protein concentrates yielded are not designed as film-forming solutions, but as protein supplements in some foods, e.g. breads, animal feeds, base for preparing milk-like beverages and the like. In other methods the objective is to prepare vital gluten powders once the solution is dried and pulverized. Finally, other methods are interested only in the separation of starch and protein from the flour.
U.S. Pat. No. 5,472,511 to Ravas et al describes a method for separating protein from grain flours which are used to form films. This method is used in the method of the present invention to provide the cross-linkable gluten polymers.